Retrograde Resection Apparatus and Method

ABSTRACT

A retrograde resection apparatus may include a cutting blade including a slot defined in the cutting blade, a recess defined in at least a portion of the slot, a screw, including a proximal end and a distal end defining a bore therethrough, a shaft having a distal end and a proximal end, wherein the shaft passes through the bore and the distal end is configured to be received in the recess, and a biasing device configured to bias the shaft against the cutting blade. In addition, the apparatus may include a tether, a first portion of which is affixed to the cutting blade and a second portion of which passes through the bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/001,473, filed Dec. 11, 2007, which claims the benefit ofU.S. Provisional Application No. 60/869,404, filed on Dec. 11, 2006, thedisclosure of which is incorporated herein by reference.

FIELD

The present disclosure relates to an apparatus and method for theresection of bone and articular cartilage, for example, for creating animplant site in an articular surface for receiving an articularprosthesis.

BACKGROUND

Articular joints may become damaged as the result of trauma, disease,wear, etc. Advancing damage to an articular joint may result in pain,loss of mobility of the afflicted joint, etc. Various techniques andsystems may be used for repairing damaged articular joints in the humanbody. One common approach for repairing a defective joint is to replacethe damaged region with a repair component. Generally a repair componentmay include a prosthetic device or a biological component.

A critical aspect of a repair procedure is the resection of at least aportion of the damaged articular cartilage and the underlying bone.Often the damaged articular cartilage is resected by opening the jointand directly drilling, cutting, or grinding away the damaged material.Such an approach typically requires at least partial separation of thejoint. Separation of the joint necessary for resecting the damagedarticular cartilage may result in attendant damage to ligaments andother connective tissues. Damage to the connective tissues of the jointmay increase the recovery time, and perhaps limit the ultimate recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the invention herein are set forth by way ofdescription of embodiments consistent with the invention. Thedescription of embodiments should be read and understood in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a perspective view of a retrograde resection apparatusconsistent with the present disclosure;

FIG. 2 depicts the use of a retrograde access tunnel in connection witha method for creating an implant site in an articular surface;

FIG. 3 depicts an initial stage of in situ assembly of the retrograderesection apparatus depicted in FIG. 1;

FIG. 4 illustrates a technique for conveying a cutting blade of theretrograde resection apparatus of FIG. 1 into a joint;

FIG. 5 shows the retrograde resection apparatus of FIG. 1 assembledwithin a joint;

FIG. 6 is a detailed view of the cutting blade assembled to the drivecomponent of the retrograde resection apparatus of FIG. 1;

FIG. 7 is a detailed, partial cross-sectional view of the cutting bladeand drive component assembly of FIGS. 1 and 6;

FIG. 8 is a partial cross-sectional view of an implant site formed inthe articular surface of a tibia using the retrograde resectionapparatus of claim 1; and

FIG. 9 is a detailed cross-sectional view of the implant site and theretrograde resection apparatus shown in FIG. 8.

FIG. 10 illustrates a cross-sectional view of an example of a retrograderesection apparatus inserted into a tibia, consistent with the presentdisclosure.

FIG. 11 illustrates a perspective view of an example of a cannulatedscrew.

FIG. 12 illustrates a perspective view of an example of a biasing memberon a drive component.

FIG. 13 illustrates a perspective view of an example of a lockingmechanism.

FIG. 14 illustrates a side view of an example of a locking mechanism.

FIG. 15 illustrates a perspective view of the locking mechanism of FIG.14.

FIG. 16 illustrates a perspective view of the drive component beinginserted into the tibia through the cannulated screw and retrogradeaccess passage, consistent with the present disclosure.

FIG. 17 illustrates a perspective view of the drive component insertedinto the tibia mated with a cutting blade.

FIG. 18a, 18b, 18c illustrates an example of a cutting blade. FIG. 18ais a perspective view from the top and FIGS. 18b and 18c are perspectiveviews from the bottom.

FIG. 19 illustrates a side view of a retrograde resection apparatus inan unbiased or uncompressed state.

FIG. 20 illustrates a side view of a retrograde resection apparatus in abiased or compressed state.

DESCRIPTION

A retrograde resection apparatus 10, depicted in FIG. 1, may be used forcreating an implant site in an articular surface of a joint by removingat least a portion of the articular surface, which may include at leasta portion of the articular cartilage of the joint surface, as well as atleast a portion of the bone underlying the articular cartilage. Theretrograde resection apparatus 10 may generally include a drivecomponent 12 and a cutting blade 14. The drive component 12 may becoupled to the cutting blade 14 to allow the cutting blade 14 to berotatably driven relative to the articular surface from a remote site.The drive component 12 may also exert an axial force on the cuttingblade 14 to direct and/or control the resection of the articularsurface.

In operation, a retrograde access passage may be formed through bone,e.g., the tibia 16 in the illustrated embodiment, behind the targetarticular surface 18. The retrograde access passage may be created bydrilling a hole through a portion of the tibia 16 from a distal positiontoward the articular surface 18, extending through the bone behind thearticular surface 18, as shown in FIG. 1. The opening 22 of the accesspassage formed in the articular surface 18 may be at, or adjacent to, adesired implant site. The trajectory of the retrograde passage may becontrolled in a free-hand manner, or using suitable drill guides, etc.Examples of suitable drill guides and procedures for creating accesspassages are shown, for example, in U.S. patent application Ser. No.10/308,718, filed Dec. 3, 2002, in U.S. patent application Ser. No.11/209,170, filed Aug. 22, 2005, and in U.S. patent application Ser. No.11/326,133, filed Jan. 5, 2006. The entire disclosures of the foregoingapplications are incorporated herein by reference.

As shown in FIGS. 3 and 4, the drive component 12 may be inserted atleast partially through the access passage, and the cutting blade 14 maybe conveyed to the drive component 12 within the joint. The cuttingblade 14 may be generally configured having a thin geometry, such as adisk or wafer. The thin geometry may allow the cutting blade 14 to beintroduced into the joint between cooperating articular surfaces withminimal separation of the joint. The relatively small amount ofseparation between the cooperating articular surfaces of the joint maylimit damage to connective tissues of the joint, such as ligaments, etc.

The cutting blade 14 may be conveyed into the joint and to the drivecomponent 12 using a tether 24, such as a flexible wire, cord, etc. Thedrive component 12 may include a cannulated shaft portion 20, which maybe inserted through the access passage so that the distal end of thecannulated shaft portion 20 protrudes above, or is at least adjacent to,the opening 22 of the access passage at the articular surface 18. Thetether 24 may be coupled to the cutting blade 14 and the tether 24 maybe pulled through the lumen of the cannulated shaft portion 20 of thedrive component 12. For example, the tether 24 may be introduced throughthe drive component 12 into the joint. A suture snare, forceps, etc.,may be used capture the tether 24 and draw it from the joint to allowthe cutting blade 14 to be attached thereto. Alternatively, the tether24 may be coupled to the cutting blade 14 and a portion of the tether 24may be introduced into the joint near the opening 22 of the accesspassage. The tether 24 may be captured by a suture snare, etc.,introduced through the lumen of the shaft portion 20 of the drivecomponent 12, and the tether 24 may be drawn through the drive component12 to convey the cutting blade 14 to the drive component 12 within thejoint.

Once the cutting blade 14 has been conveyed into the joint, the drivecomponent 12 may be drivingly coupled to the cutting blade 14, as shownin FIG. 5. With additional reference to FIGS. 6 and 7, the cutting blade14 may define a radial slot 26. An inner shaft portion 28 of the drivecomponent 12 may be sized to be received in the slot 26 of the cuttingblade 14. The cutting blade 14 may, therefore, be assembled to the drivecomponent 12 by sliding the cutting blade 14 onto the inner shaftportion 28 of the drive component 12.

In an embodiment, rather than conveying the cutting blade to the drivecomponent within the joint using a tether, the cutting blade may beinserted into the joint and installed on the inner shaft portion of thedrive component using tweezers, forceps, etc. For example, the cuttingblade may be grasped by forceps and inserted into the joint with theslot of the cutting blade oriented to receive the inner shaft portion ofthe drive component. The cutting blade may be installed on the innershaft portion and released by the forceps. Various similar techniquesmay be used for conveying the cutting blade into the joint andassembling the cutting blade to the drive component.

The drive component 12 and the cutting blade 14 may include interactingfeatures for transmitting torque from the drive component 12 to thecutting blade 14, e.g., to allow the cutting blade 14 to be rotatablydriven by the drive component 12. In the illustrated embodiment, theinner shaft 28 of the drive component 12 may include one or moreprotrusions 30, 32 which may be received in corresponding recesses 34,36 in the cutting blade 14. The protrusions 30, 32 may be semi-sphericalprotrusions, as illustrated, cylindrical members, e.g., in the form of apin extending radially across the shaft portion, etc. The cutting blade14 may include a central hub 38, and the recesses 34, 36 may be formedas axially extending slots in the hub 38. As shown in FIGS. 5 through 7,the cutting blade 14 may be slidingly received on the inner shaftportion 28 of the drive component 12 with the protrusions 30, 32 abovethe hub 38. The protrusions 30, 32 and the recesses 34, 36 may bealigned and the cutting blade 14 and the inner shaft 28 may be moved toengage the protrusions 30, 32 in the recesses 34, 36.

An outer sleeve 40 of the drive component 12 may be slidingly disposedrelative to the shaft portion 28. The sleeve 40 may be positioned toengage a bottom surface 42 of the cutting blade 14 and may maintain theengagement of the protrusions 30, 32 in the recesses 34, 36.Additionally, the engagement between the sleeve 40 and the bottomsurface 42 of the cutting blade 14 may generally align the cutting blade14 relative to the drive component 12, e.g., so that the cutting blade14 is generally perpendicular to the drive component 14. The alignmentbetween the cutting blade and the drive component, however, is notnecessary.

The sleeve 40 may be biased toward the distal end of the inner shaftportion 28, e.g., a forward position. The sleeve 40 may be retractedaway from the end of the shaft portion 28 to expose at least a portionof the shaft portion 28 to allow the cutting blade 14 to be received onthe shaft portion 28 proximal to the protrusions 30, 32. The sleeve 40may then be urged toward the forward position to urge the drivecomponent 12 into engagement with the cutting blade 14 and to maintainthe engagement thereof. For example, a handle 44 may be coupled to thesleeve 40 for sliding the sleeve 40 to a retracted position relative tothe shaft portion 28. The sleeve 40 may be biased toward the forwardposition using any suitable biasing element, e.g., a spring, actingagainst the sleeve 40, the handle 44, etc. Rather than being biased, orin addition to being biased, the sleeve may be movable between theretraced and the forward positions and may be engaged, or locked, in atleast the forward position, if not in both positions.

Referring also to FIGS. 8 and 9, with the drive component 12 drivinglycoupled to the cutting blade 14, an implant site 48 may be formed byresecting at least a portion of the articular surface 18. The cuttingblade 14 may be rotatably driven by the drive component 12, which may bedriven by a drill or other suitable drive device. As shown, e.g., inFIGS. 6 and 7, the cutting blade 14 may include one or more cuttingfeatures 50, 52. The cutting features may include downwardly projectingblades, etc. As the cutting blade 14 is rotatably driven by the drivecomponent 12, the cutting blade 14 and the drive component 12 may bemoved in a retrograde direction, urging the cutting blade 14 into thearticular surface 18 to resect at least a portion of the articularsurface 18 to create the implant site 48. The cutting features 50, 52may cut, grind, shave, etc., contacted articular cartilage, bone, etc.to create the implant site 48.

With particular reference to FIG. 9, in an embodiment in which thesleeve 40 is urged into engagement with the bottom surface of thecutting blade 14, the cutting blade 14 may be generally orientedperpendicularly to the axis of the drive component 12. Correspondingly,the resected implant site 48 may generally be oriented coaxial with thedrive component 12.

FIG. 10 illustrates another example of a retrograde resection apparatus110 contemplated herein. The apparatus 110 includes a drive component,such as an elongate shaft 112, including a proximal portion 114 and adistal portion 116. A cutting blade 118 may be mounted on the distalportion of the shaft 112. A cannulated screw 120 may be provided forreceiving the shaft and providing a stopping mechanism for the cuttingblade during resection. In addition, a biasing device 130, may bepositioned on the shaft 112 to bias the shaft against the screw 120and/or the cutting blade 118.

As illustrated in FIG. 11, the cannulated screw 120 may include a screwhaving a bore passing there through. A distal portion 121 of the screwmay include a tap 122 or a number of discontinuous threads for cuttingthreads into the bone. The screw may also include a plurality ofcontinuous threads 124 covering at least a portion of the screw, nearthe center 123 of the screw. To facilitate turning the screw, a nut 126may be provided towards the proximal portion 125 of the screw. Thus, inoperation, after a retrograde access passage has been formed, one mayturn the screw into the bone, tapping the threads and feeding the screw120, until the screw 120 reaches a desired location or height in thebone proximate to the joint surface. Once the screw 120 is in place, thedrive component 112 may be fed through the screw bore and up to thetibia plateau, as illustrated in FIG. 10.

The biasing device 130, illustrated in FIG. 12, may include a lockingmechanism 132, a spring 134 and one or more sleeves 136, 138, whereinthe spring and sleeves may extend between the locking mechanism 132 andthe cutting blade 118. The locking mechanism 132 may slidably move upand down the drive component 112 to position the sleeves 136, 138 alongthe drive component and compress the spring 134. One example of alocking mechanism may include, for example, a bayonet connector,illustrated in FIG. 13. The bayonet connector may include a ring orcylinder 140. The interior surface of the ring or cylinder may include afirst channel 142 defined therein along the axis A-A of the drivecomponent 112. This channel may be defined in the entire length of thelocking member 132. A stem 144 located on the drive component 112 maypass through the first channel 142 as the locking mechanism 132 ispositioned on the drive component 112.

A second notch or channel 146 may be provided in the interior surface ofthe locking mechanism 132 to receive the stem 144, placing the biasingdevice 130 in the locked position. The second channel 146 may be definedin only a portion of the locking mechanism 132 surface, i.e., thechannel does not pass through the entire length of the locking mechanism132. In one example, the second channel 146 may include an opening onthe proximal side 147 of the locking mechanism and the stem may seat inthe second channel. It may be appreciated that this channel may alsoinclude a number of other configurations. For example, a first portionof the channel may be defined along axis A-A of the shaft and a secondportion may turn at an angle to the first portion. Furthermore, inanother example, the channel may include one or more continuous femalethreads through a portion of the length of the locking mechanism. It mayalso be appreciated that in other embodiments a channel may be provided,beginning on the distal end 147 of the locking mechanism, for receivingthe stem 144.

While the locking mechanism 132 is illustrated in FIGS. 12 and 13 asbeing circular in shape, it may be appreciated that the outer diameterof the locking device may be any geometry, such as square, elliptical,rectangular, etc. In addition, the outer surface of the lockingmechanism may also include nubs 148 having a raised profile with respectto the remainder of the surface. The nubs 148 may facilitate the user inmoving of the locking mechanism about the drive component 112.

Another example of a locking mechanism 132 is illustrated in FIGS. 14and 15. The locking mechanism may include a base portion 150 and atleast two flexible legs 152, 154 extending from the base portion 150around the drive component 112. Flexible may be understood herein ascapable of being compressed and substantially returning to theiroriginal shape. To increase flexibility, a slot 153 may be defined in aportion of the legs proximate to the base The legs may also include aridge 156, 158, which may be received in recess 160 in the drivecomponent 112. Applying a force F to both sides of the legs 152, 154 maycause the legs to flex inward and away from the drive component 112,removing the ridges 156, 158 from the recess 160 and allowing thelocking mechanism to slide up and down the drive component 112.

Referring back to FIG. 12, the biasing device 130 may also include afirst sleeve 136, which may be received near the distal end of the drivecomponent 112. The first sleeve may pass through the cannulated screw120 and abut the bottom surface of the cutting blade 118. A secondsleeve 138 may also be provided, which may form a portion of the lockingmechanism 132 or may abut the locking mechanism 132. In the presentexample, a spring 134 may be positioned between the two sleeves 136,138. The spring may include a stop 135, such as a disc or washer on thedistal end, wherein the stop 135 may be received by or abut the nut 126of the cannulated screw 120. It may be appreciated that the spring 134may also pass within and be received inside of the second sleeve 138. Inaddition, it may also be appreciated, that a number of otherspring/sleeve combinations may be contemplated, for example one springand one sleeve may be provided wherein the spring abuts the lockingmechanism and the sleeve is positioned between the spring and thecutting blade.

Accordingly, once the cannulated screw 120 is in place, as describedabove, one may insert the distal end 116 of the drive component 112 intothe resection access passage and through the cannulated screw 120, asillustrated in FIG. 16. The cutting blade 118 may then be fed into thejoint proximal to the drive component 112 and positioned on the drivecomponent 112, as illustrated in FIG. 17. It may be appreciated that toposition the cutting blade 118, one may use a pair of forceps, dulltweezers or other devices. In addition, one may also attach a tether,such as a suture or thread, to the cutting blade 118 and feed the tetherthrough the resection access path and the cannulated screw 120 boreprior to inserting the drive component 112.

The cutting blade 118, illustrated in FIGS. 18a, 18b and 18c , mayinclude a body 172 having a number of cutting features 174 extendingfrom a bottom surface 173 of the body. The cutting blade 118 may berelatively thin, having a thickness of less than 1 mm, including allvalues and increments in the range of 1 mm to 0.1 mm. The cutting blademay also include a slot 176 cut through the entire thickness of thecutting device in at least a portion of the cutting blade 118. The slot176 may have a first portion 178, radially extending from the center ofthe cutting blade 118 to an edge of the cutting blade. The slot 176 mayalso have a second portion 180, positioned near the center of thecutting blade 118. The second portion 180 of the slot 176 may be definedin a hub 182, which may extend from the top and/or bottom surface of thecutting device. Defined within the hub 182 and the second portion of theslot 180 may be one or more recesses 184. The recesses 184 may receivethe distal portion 116 of the drive component 112 illustrated in FIG.12. In one example, the drive component 112 may include twohemispherical projections 119, which may slidably be positioned withinthe recesses 184. In addition, it may be appreciated that the distalportion 116 of the drive component may be sized so as to pass throughthe slot 176.

The cutting features 174 of the cutting blade 118 may include a lip orblade 186, which projects from the bottom surface of the cutting blade,for removing the bone and any auxiliary tissue. Each cutting feature mayalso include a slit 188. The slits 188 may pass through the body of thecutting blade at an angle a to the height of the blade, through whichdebris may pass as resection proceeds.

Once the drive component 112 and cutting blade 118 are mated, thebiasing device 130 may be positioned. As illustrated in FIGS. 19(illustrating the biasing device uncompressed) and 20 (illustrating thebiasing device compressed), the first shaft 136 may be arranged withinthe cannulated screw 120 and abut the cutting blade 118. As force F isapplied in the axial direction on the locking mechanism 132 of thebiasing device, the spring 134 may compress against the cannulated screw120 and/or the first shaft 136 as well as the second shaft 138 until thelocking member 132 is locked in position.

Once the locking member 132 is locked in position along the drivecomponent 112, a radial force, or torque may be applied to the proximalend of the drive component 112, providing rotation of the cuttingdevice. It may be appreciated that the cutting blade 118, may exhibitpolyaxial movement, i.e., the cutting blade may move, not only along theaxis of the drive component, but may rotate at an angle β to the drivecomponent as well. For example, the cutting blade 118, may besubstantially planar with the tibial plateau and at an angle β in therange of approximately 10 degrees to 80 degrees to the drive componentalong axis A-A. However, once resection is complete, the angle β of thecutting blade may be in the range of 20 degrees to 90 degrees to thedrive component along axis A-A.

Consistent with the foregoing, according to one aspect, the presentdisclosure may provide a retrograde resection apparatus for creating animplant site in an articular surface of a joint. The retrograderesection apparatus may include a cutting blade and a drive component.The cutting blade may be a disk or wafer and having cutting featuresextending from, or located on, the bottom surface of the cutting blade.The cutting features may be configured to resect material adjacent tothe bottom surface of the cutting blade. The drive component may beconfigured to be releasably coupled to the cutting blade and may includea shaft for rotatably driving the cutting blade. The cutting blade mayinclude a radial slot sized to receive at least a portion of the shaftof the drive component. The cutting blade may, therefore, be assembledto the shaft of the drive component in situ within the joint by slidingthe cutting blade onto the shaft via the slot in the cutting blade. Thecutting blade and the drive component may include cooperating featuresallowing the shaft of the drive component to be coupled to the cuttingblade for transmitting torque and axial thrust to the cutting blade. Inan embodiment, the cooperating features may include radial protrusionson the shaft and recesses in a hub of the cutting blade configured to atleast partially receive the protrusions.

According to another aspect, the present disclosure may provide a methodfor creating an implant site in an articular surface of a joint. Themethod may generally include creating a retrograde access passage to thearticular surface through bone behind the articular surface. A shaft ofa drive component may be inserted though the access passage and acutting blade may be conveyed to the shaft and may be assembled to theshaft to allow the shaft to rotatably drive the cutting blade and toapply an axial thrust on the cutting blade. The cutting blade may berotatably driven by the shaft and may be urged into the articularsurface. A portion of the articular surface may be resected by cuttingfeatures extending from, or located on, the bottom of the cutting bladeas the cutting blade is rotated and urged into the articular surface ina retrograde direction.

While the present invention has been set forth above by way ofembodiments consistent therewith, the described embodiments aresusceptible to numerous modifications and variations without materiallydeparting from the invention. All such modifications and variations areconsidered to be within the scope of the present invention.

What is claimed is:
 1. A retrograde resection apparatus, comprising: a cutting blade having a body defining a first surface and a second surface, including at least one cutting feature provided on said second surface; a slot defined through at least a portion of said body; a recess defined in at least a portion of said slot; a shaft having a distal end and a proximal end, wherein a portion of said distal end is received in said recess; and a biasing device configured to bias said shaft against said cutting blade.
 2. The apparatus of claim 1, further comprising: a hemispherical protrusion extending from said distal end of said shaft, wherein said protrusion is configured to be at least partially received in said recess.
 3. The apparatus of claim 1, wherein at least a portion of said distal end of said shaft is configured to be received in said slot.
 4. The apparatus of claim 1, further comprising a screw, including a proximal end and a distal end defining a bore therethrough, received on said shaft.
 5. The apparatus of claim 4, wherein said shaft is rotatable in said bore.
 6. The apparatus of 4, wherein said screw includes a nut on said proximal end
 7. The apparatus of claim 4, wherein said screw includes a plurality of continuous threads in a central portion and a tap proximate said distal end.
 8. The apparatus of claim 1, further comprising: a first sleeve slidably positioned on said shaft; a spring slidably positioned on said shaft between said first sleeve and said biasing member.
 9. The apparatus of claim 1, wherein said shaft includes a stem and said biasing member includes a ring including an interior surface having a channel defined therein for receiving said stem.
 10. The apparatus of claim 9, wherein said channel includes a first portion extending along the axis of said shaft and a second portion extending in a direction at an angle from the axis of said shaft.
 11. The apparatus of claim 9, wherein said ring comprises a first sleeve extending from said ring, and said apparatus further comprises a spring supported by said first sleeve and a second sleeve positioned between said spring and said cutting blade and upon biasing said ring, said spring is compressed and a force is transmitted to said cutting blade.
 12. The apparatus of claim 1, wherein said shaft includes a recess defined therein and said biasing member includes a collar positioned on a portion of said shaft, wherein said collar includes a ridge for being received in said recess defined in said shaft.
 13. The apparatus of claim 12, wherein said collar includes a base and flexible legs extending from said base and said ridge is positioned on at least one of said legs and wherein said ridge in a first position is received in said recess defined in said shaft and upon flexing said flexible legs said ridge is configured to be removed from said recess.
 14. The apparatus of claim 1, further comprising a tether, wherein said tether is affixed to said cutting blade.
 15. The apparatus of claim 1, wherein said cutting blade is non-rotatable with respect to said shaft when said distal end is received in said recess.
 16. The apparatus of claim 1, wherein said cutting blade is tiltable at an angle defined by the axis of said shaft and a surface of said cutting blade.
 17. The apparatus of claim 1, wherein said cutting blade body is less than 1 mm in thickness.
 18. The apparatus of claim 1, wherein the cutting blade body defines an edge, said cutting blade body has a first thickness and said body tapers to a second thickness proximate to said edge.
 19. The apparatus of claim 1, wherein said cutting feature includes a lip extending from said second surface of said body and a slit defined through said body at an angle to the second surface of the cutting device.
 20. A retrograde resection apparatus, comprising: a cutting blade having a body defining a first surface and a second surface, including a cutting feature extending from said second surface; a slot defined in said cutting blade; a recess defined in at least a portion of said slot; a screw, including a proximal end and a distal end defining a bore therethrough; a shaft having a distal end and a proximal end, wherein said shaft passes through said bore and said distal end is configured to be received in said recess; a biasing member configured to bias said shaft against said cutting blade; and a tether, a first portion of which is affixed to said cutting blade and a second portion of which passes through said bore. 